The present invention relates to a method of and an arrangement for crimping of synthetic fibers, by means of rotatable compression rolls which supply a cable to a compression chamber with high speed, and wherein cooling air is blown into a housing which surrounds the compression rolls during operation.
Methods and arrangements of the above-mentioned general type are known in the art. In known methods and arrangements, a cable of freshly spun fibers of synthetic polymers is stretched in a continuous working process, is crimped in a compression chamber and subsequently cut to staple fibers. The crimping speed which is equal in conventional discontinuous processes to at most 100-150 m/min and does not exceed in practice 300 m/min must be naturally adjusted in a continuous process to the spinning speed and lies therefore always over 500 m/min, as a rule even over 1,000 m/min. With a typical spinning speed of 500 m/min and a stretching ratio of 1:4, a speed of 2,000 m/min is obtained for the stretched cable. With this speed, the cable is supplied to the crimping arrangement. At this speed the supply rolls of the crimping chamber, with the diameter of, for example, 120 mm, have a rotary speed of more than 5,000 rev/min. The modern developments have a tendency to have even higher speeds.
The given number of revolutions is counted from the condition that the surface speed of the rolls is equal to the supply speed of the cable. In contrast, the speed with which material moves forwardly in the compression chamber is considerably smaller. As a result of this, in addition to heat which is produced by the compression process, a friction heat takes place at the contact locations between the rolls and the material and it must be counted more and more with increasing speed. On the other hand, the cable whose temperature is increased by the produced heat, continuously withdraws heat. Computations and estimates show that the compression heat proper is withdraw at high speeds mainly through the cable, without exceeding the permissible value of its temperature. This is however no longer true to full extent for the above-mentioned friction heat. Cooling is required for this heat.
In the U.S. patent application Ser. No. 647,132, a crimping arrangement for high speeds is described, which is protected by a complete casing from outer influences. By blowing of cooling air into the housing, the temperature is easily controllable. The cooling air passes through the housing over a predetermined path and provides a uniformly maintained sufficient cooling. It has been shown, however, that air cooling is not sufficient in all cases to withdraw high friction heat.
The DE-OS No. 1,660,637 discloses a crimping arrangement in which additionally to a surface cooling, air provides an inner cooling of the compression rolls. It however requires conduits for supplying a cooling medium into the interior of the compression rolls, which is connected with especially complicated sealing problems in high speed crimping arrangements. It is structurally impossible to arrange cooling medium passages in the compression rolls. Since in contrast to the conventional crimping arrangements which operate with Titers up to 4 Mio Dtex, in the fast modern machines only Titers up to 200,000 Dtex take place, the compression rolls are correspondingly small and rather disc-shaped.
The U.S. Patent No. 2,862,279 discloses a crimping arrangement with a horizontal feed, in which water is supplied for cooling into the gap between the rotatable compression rolls and the fixed chamber walls. This arrangement can be used for the speeds of approximately 45 m/min or approximately 110 m/min when the water is sprayed with sufficiently high pressure. In the event of considerably higher speeds, no sufficient cooling can be obtained in this manner. The sprayed water is flung unused in its main part from the surfaces of the rolls. The water which is sprayed into the vent-shaped gap between the rolls and both horizontally arranged chamber walls is conveyed because of the high surface speed of the rolls from this gap and does not contact the cable. A further disadvantage is that it is necessary to provide a complicated arrangement of several nozzle pipes which partially must be provided at hardly accessible locations. Since there is always the danger that fine nozzle openings are clogged, it is very difficult to guarantee with this arrangement a uniform, finely dosed cooling.